Density functional studies on lanthanide (III) texaphyrins (Ln-Tex2+, Ln = La, Gd, Lu):: structure, stability and electronic excitation spectrum

Density functional calculations have been performed to study the molecular structure and chemical properties of selected lanthanide(III) texaphyrins (Ln-Tex(2+), Ln=La, Gd, Lu). The lanthanide element is found to reside above the mean N-5 texaphyrin plane, and the larger the cation, the greater the observed out-of-plane displacement. It is concluded that the lanthanide cation is tightly bound to the macrocyclic skeleton, yielding a stable structure. However, the chemical properties of Ln-Tex(2+) are found to be only slightly affected by the substitution of the lanthanide element. A low-energy LUMO is found for the Ln-Tex(2+) (Ln=La, Gd, Lu), which are therefore easily reduced in an electron-rich environment. Two characteristic bands are obtained in the calculated electronic excitation spectrum (a high-energy band at 454-462 nm and a low-energy band at 681-686 nm). The intensity of the high-energy band is much larger than that of the low-energy one, yielding a rather unique spectral feature.